This invention relates to amorphous magnetic alloys that can be readily produced and have superior mechanical properties and superior corrosion resistance.
In recent years, advances made in the progress of super-rapid cooling or super-quenching technology have made it possible to produce a variety of amorphous magnetic alloys. There are reports in the literature that amorphous alloys, such as Fe--P--C, Co--P--B, Ni--B, etc., have been produced by the gun method, piston anvil method and splat quenching method of. It is known that amorphous alloys can be obtained by combining P, C and B with transition metals. Of these elements, P raises the problems that, because of its low vapor pressure, when producing a P-containing alloy it is liable to shift the P content from a desired value and to bring about environmental pollution. On the other hand, C poses the problem that difficulties are encountered in dissolving it into a transition metal during melting to form solid solution thereof and in achieving separation and precipitation of the solid solution, thereby making production difficult. Thus, B is known as the most promising element today. The aforesaid production methods of the prior art have given way to a double roll process or a single roll process which is now the mainstay of the methods for producing amorphous magnetic alloys. This is because, while the methods of the past have only enabled amorphous alloys to be obtained in unstable thin pieces, the double roll and single roll processes enable amorphous magnetic alloys to be produced in a ribbon form of constant width and thickness, so that the double and single roll processes have great advantages in industrial viewpoint.
The double roll process is higher than the single roll process in the ability to render molten metal amorphous because the former converts an alloy in molten form into an amorphous state by rolling and rapid cooling carried out from both sides of the alloy in molten metal form while the latter carries out cooling from one side only. However, the double roll process suffers the disadvantage that, since rolling and rapid cooling of an alloy in molten metal form are carried out, the surfaces of the rolls are liable to be damaged and great difficulties are encountered in obtaining an amorphous alloy in an elongated strip form of large width and length. Thus, the present condition is such that the single roll process has to be relied on in view of producing amorphous alloys on a mass production basis.
The single roll process now available is capable of producing amorphous alloys in the form of ribbon of a large width or a width of about 20 cm while the double roll process produces amorphous alloys in the form of ribbon of a width of no more than 2 cm. This can be accounted for by the fact that, while in the single roll process the apparatus can be made ready for the production of large width ribbon merely by increasing the width of the single roll, it is necessary in the double roll process not only to increase the width of the two rolls but also to increase the horse power of the motor and the strength of the bearings for carrying out rolling, thereby rendering the apparatus larger in scale. Further, as is well known, amorphous magnetic alloys have very high hardness, so that it is quite difficult to avoid damage of the surfaces of the rolling rolls used in the double roll process. In the single roll process, on the other hand, molten metal is merely blown against the surface of the single roll to obtain rapid cooling thereof, so that the roll surface is free from damage. In view of this characteristic, the single roll process is the mainstay for producing amorphous magnetic alloys because the alloys can be produced on a mass production basis by this process, despite low rapid cooling ability.
By the way, amorphous magnetic alloys of the composition containing a transition metal and boron can be readily produced in ribbon form with a width of about 1 cm by the double roll process, but the single roll process has been capable of only producing the alloys in ribbon form with a width of about 1-2 mm. When an attempt is made to increase the width, the temperature of the ribbon is 400.degree.-600.degree. C. when the solidified ribbon is released from the roll and wound because in the single roll process cooling is not effected sufficiently. Thus, the ribbon obtained is oxidized and turns yellow in color. The amorphous magnetic alloys obtained in this way have been very brittle, and they lack the mechanical properties of withstanding 180 degree bending inherently residing in amorphous alloys. Because the amorphous alloys are not only low in mechanical properties but also the alloys in ribbon form are partly crystallized, their magnetic properties also are not as they should be. Thus, difficulties have hitherto been encountered in obtaining amorphous magnetic alloys of the (Fe--Co--Ni)--B system of good properties in the form of ribbon of large width by the single roll process.
Amorphous magnetic alloys of the (Fe--Co--Ni)--Zr system and the (Fe--Co--Ni)--Zr--B system which are improvements on the (Fe--Co--Ni)--B system have since been developed. These materials can be more readily produced in the form of amorphous ribbon of large width by the single roll process than the alloys of the (Fe--Co--Ni)--B system. However, the alloy systems containing zirconium are liable to be oxidized, and it is quite difficult to melt a master alloy and rapidly cool the molten metal in the air by the single roll process, to obtain an amorphous alloy. Because of this, production of amorphous alloys is carried out in vacuum or inert gas atmosphere. However, this raises the problem of low productivity and high cost.
Amorphous alloys of the (Fe--Co--Ni)--Si--B system, (Fe--Co--Ni)--P--B system and (Fe--Co--Ni)--P--C system have also been known to be comparatively readily produced in the air in the form of ribbon. However, these alloys have been found to be low in wear resistance with respect to tape when these alloys have been made into magnetic head cores. This is a serious defect of amorphous alloys when one considers that amorphous alloys can have application in magnetic core heads by utilizing their soft magnetic properties.